We have shown that v-Abl initiates a signal transduction which leads to activation of Ras, Raf and cyclin dependent kinases (Cdks) with subsequent hyperphosphorylation of Rb family proteins, activation of E2F/DP proteins and induced transcription of E2F-dependent genes including c-myc and DHFR. Since our results show that v-Abl has direct effects on cell cycle, it is important to characterize fully how v-Abl and BCR-ABL affect cell cycle and to assess the importance of cell cycle regulation for Abl-dependent transformation. Cell cycle regulation is central to growth regulation and therefore understanding these mechanisms is critical to understanding molecular mechanisms of Abelson transformation. In the first Specific Aim, fibroblast and preB cells transformed with a temperature sensitive form of v-Abl will be analyzed to determine how v- Abl will be analyzed to determine how v-Abl affects cell cycle regulation. Three important aspects of cell cycle regulation will be studied: 1) the cellular concentration of cyclins and Cdk inhibitors, 2) Cdk2 and Cdk4 activity and 3) induction of E2F- and c-Myc-dependent mRNAs. In Specific Aim II, we will test the hypothesis that v-Abl signaling which depends upon Abi-l or Jaks affects cell cycle regulation. Cell lines generated by the Goff and Rothman groups which have detected signaling by Abi-l or Jaks will be compared to normal cells for v-Abl-dependent cell cycle regulation. In Specific Aim II the ability of BCR-ABL to affect cell cycle will be studied by analyzing primary samples samples from CML patients and by studying cell lines transformed with temperature sensitive bcr-abl. The last section of the proposal is designed to test the functional importance of cell cycle regulation of cell cycle regulation for transformation by V-Abl and BCR- ABL. We will test the hypothesis that impaired cell cycle regulation makes more susceptible to Abelson transformation, that the pro/preB cell preference of v-Abl transformation may be determined in part by aspects of cell cycle regulation and that v-Abl transformed lines may harbor mutations in genes whose products regulate cell cycle.